There are combine harvesters in which the cutterbar assembly can be lifted and lowered by means of two single-acting hydraulic piston and cylinder units. To lift the harvesting attachment, the two cylinder chambers of the hydraulic piston and cylinder units on the piston face side admit oil, whereas during the lowering operation the piston rods are retracted simply by the weight of the cutterbar assembly. When working in the field, the cutterbar assembly is adjusted in such a way that the finger bar has a predetermined distance from soil in a field. Additional spring assemblies assist the hydraulic piston and cylinder units and allow a certain springing of the cutterbar assembly when used in the field. In their front region, the known cutterbar assemblies have sensing devices by which an electromagnetic control valve is switched on for detection of an obstacle in such a way that the two cylinder chambers on the piston face side admit oil in order to lift the cutterbar assembly above the obstacle. This known manner of lifting a cutterbar assembly has the drawback that, if obstacles occur suddenly, the assembly cannot be lifted out of the way quickly enough. This is due to the fact that in order to carry out rapid lifting, a very large oil stream must be suddenly provided, however, the quantity of oil, which is absolutely required is relatively small in this case. The risk of not being able to lift the cutterbar assembly quickly enough when obstacles arise increases in relationship to the travelling speed of the combine harvester.
In an aspect of this invention, a harvesting machine with a front-mounted harvesting attachment that is pivotable about a shaft running transversely to the direction of travel and capable of lifting when an obstacle is detected is disclosed. This apparatus includes a sensing device with at least one double-acting hydraulic piston and cylinder unit, having a first cylinder chamber and a second cylinder chamber, arranged on the harvesting attachment, a control valve associated with the sensing device in such a way that when the sensing device is not operated, the first cylinder chamber is in fluid communication with the second cylinder chamber by a control valve and when the sensing device is operated, fluid communication between the first cylinder chamber and the second cylinder chamber is interrupted by the control valve.
In another aspect of this invention, a method for lifting a front-mounted harvesting attachment that is pivotable about a shaft running transversely to the direction of travel when an obstacle is detected is disclosed. The method includes operating a control valve associated with a sensing device, with at least one double-acting hydraulic piston and cylinder unit, having a first cylinder chamber and a second cylinder chamber, arranged on the harvesting attachment in such a way that when the sensing device is not operated, the first cylinder chamber is in fluid communication with the second cylinder chamber by a control valve and when the sensing device is operated, fluid communication between the first cylinder chamber and the second cylinder chamber is interrupted by the control, valve.
Some of the advantages of this invention, but not all by any means, are achieved according to the invention by the fact that the hydraulic piston and cylinder unit is double-acting and, when the sensing device is not operated, the first cylinder chamber on the piston face side communicates with the second cylinder chamber on the piston rod side by the control valve via lines, wherein between the second chamber of the cylinder on the piston side and the electromagnetic control valve is provided an accumulator and, when the sensing device is operated, the communication between the first and second cylinder chambers is interrupted by the control valve with the second chamber of the cylinder on the piston rod side connected to a tank. Advantageously, in this case, the accumulator in the pressurized state contains at least the quantity of oil needed for the necessary extension of the piston rod of the hydraulic piston and cylinder unit.
This solution has the advantage that there are no extra spring assembles required because, when the first and second cylinder chambers are short-circuited with each other during use, the accumulator can function as a spring assembly. But an additional advantage lies in that the whole system is pressurized so that when the communication between the two cylinder chambers is interrupted, on account of the variation in surface conditions, there is a sudden increase in power because only the first cylinder chamber on the piston face side is subjected to the pressure applied, while the oil which is in the second cylinder chamber on the piston rod side can flow back without pressure to the tank. Consequently, a cutterbar assembly is lifted after detection of an obstacle immediately and without delay.
These advantages are not to be construed as all-inclusive, but are just many of innumerable advantages associated with the present invention.